Large area suspended graphene for nano-mechanical devices

To address the need for large area dry graphene transfer techniques in Nanomechanical applications we use transfer printing to suspend large areas of graphene on pre-patterned substrates with cavities. We find that using this method, clean suspended graphene can be produced with areas up to 15 x 15 mu m(2). (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinhei

Graphene quantum capacitors for high-Q tunable LC-tanks for RF ICs

We propose and characterize graphene quantum capacitors, tunable with voltage by the control of their charge density, for tunable LC tanks as essential building blocks for Radio-Frequency (RF) functions in densely integrated circuits. We fabricate and investigate their performance in RF, and we demonstrate quantum capacitances, C-q, in the range of pF with a tuning range of >1.3:1 within 1.25 V, with Q-factors up to 14.5 at 0.4 GHz. Our capacitors have a high capacitance density, up to 2.65 fF/mu m(2), which is 100x higher than the one of RF MEMS capacitors. Based on calibrated models and simulations, we demonstrate the potential to replace their semiconductor counterparts and RF MEMS capacitors in LC tanks, for key RF analog application

Graphene Quantum Capacitors for High Frequency Tunable Analog Applications

Graphene quantum capacitors (GQC) are demonstrated to be enablers of radio-frequency (RF) functions through voltage-tuning of their capacitance. We show that GQC complements MEMS and MOSFETs in terms of performance for high frequency analog applications and tunability. We propose a CMOS compatible fabrication process and report the first experimental assessment of their performance at microwaves frequencies (up to 10 GHz), demonstrating experimental GQCs in the pF range with a tuning ratio of 1.34:1 within 1.25 V, and <i>Q</i>-factors up to 12 at 1 GHz. The figures of merit of graphene variable capacitors are studied in detail from 150 to 350 K. Furthermore, we describe a systematic, graphene specific approach to optimize their performance and predict the figures of merit achieved if such a methodology is applied

Field-enhanced design of steep-slope VO2 switches for low actuation voltage

The abrupt metal-insulator transition in vanadium dioxide (VO2) offers novel performance and functionality for beyond CMOS switches, enabling simultaneous high ON current and ultra-steep subthreshold slope with low temperature dependence. We developed a field-enhanced design of 2-terminal VO2 switches that allows decreasing their actuation voltage without affecting their performance and reliability. Exploiting this design, we characterized VO2 switches with extremely abrupt transitions (< 1 mV/dec) until 60 degrees C and a reduction in actuation voltage up to 38.3% with respect to conventional devices

Biogeochemical mechanisms controlling trophic state and micropollutant concentrations in a tropical artificial lake

Universidade de Brasília. Instituto de Geociências. Brasília, DF, Brazil.Universidade de Brasília. Instituto de Geociências. Brasília, DF, Brazil.Universidade Federal de Tocantins. Departamento de Química Ambiental. Tocantins, TO, Brazil.Universidade de Brasília. Instituto de Geociências. Brasília, DF, Brazil.Companhia de Saneamento do Distrito Federal. Brasília, Df, Brazil.Ministério da Saúde. Secretaria de Vigilância em Saúde. Instituto Evandro Chagas. Ananindeua, PA, Brasil.Universidade de Brasília. Instituto de Geociências. Brasília, DF, Brazil.Lake Paranoá is a human-made water reservoir created in 1959 together with the new capital of Brazil (Brasilia). With the demands of urban development, population growth, and land use changes, the lake presented severe deterioration of water quality due to the disposal of wastewater with a high concentration of nutrients. To better elucidate the natural and anthropogenic sources controlling the water quality from Lake Paranoá, this study aimed to (1) investigate the main geochemical processes controlling water quality of the lake and its tributaries; (2) evaluate Lake Paranoá’s trophic state; and (3) determine the occurrence and fate of organic micropollutants in Lake Paranoá waters and WWTPs effluents. The waters from Lake Paranoá tributaries are naturally acidic due to the nature of the extremely weathered ferralsols and the crustal material composition. The main processes linked with anthropogenic activities that affect the water quality from the tributaries are the input of untreated domestic wastewater and the dissolution of carbonate minerals arising from construction material residues. Generally, the waters of Lake Paranoá presented low nutrient and chlorophyll-a concentrations, indicating a low trophic state (oligo-mesotrophic). A significant increase in the trophic state (super-eutrophic) was observed at specific regions of the lake that have high nutrient input from tributaries, caused by the continuous disposal of untreated domestic sewage. In Lake Paranoá waters, the organic micropollutants that were identified and quantified (caffeine, bezafibrate, bisphenol A, diethyl phthalate, and nonylphenol) presented concentrations consistent with previous studies and within the threshold of toxicity, except bisphenol A